Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
SU(1)			FreeBSD	General	Commands Manual			 SU(1)

     su	-- substitute user identity

     su	[-] [-c	class] [-flms] [login [args]]

     The su utility requests appropriate user credentials via PAM and switches
     to	that user ID (the default user is the superuser).  A shell is then

     PAM is used to set	the policy su(1) will use.  In particular, by default
     only users	in the ``wheel'' group can switch to UID 0 (``root'').	This
     group requirement may be changed by modifying the ``pam_group'' section
     of	/etc/pam.d/su.	See pam_group(8) for details on	how to modify this

     By	default, the environment is unmodified with the	exception of USER,
     HOME, and SHELL.  HOME and	SHELL are set to the target login's default
     values.  USER is set to the target	login, unless the target login has a
     user ID of	0, in which case it is unmodified.  The	invoked	shell is the
     one belonging to the target login.	 This is the traditional behavior of
     su.  Resource limits and session priority applicable to the original
     user's login class	(see login.conf(5)) are	also normally retained unless
     the target	login has a user ID of 0.

     The options are as	follows:

     -c	class
	     Use the settings of the specified login class.  The login class
	     must be defined in	login.conf(5).	Only allowed for the super-

     -f	     If	the invoked shell is csh(1), this option prevents it from
	     reading the ``.cshrc'' file.

     -l	     Simulate a	full login.  The environment is	discarded except for
	     HOME, SHELL, PATH,	TERM, and USER.	 HOME and SHELL	are modified
	     as	above.	USER is	set to the target login.  PATH is set to
	     ``/bin:/usr/bin''.	 TERM is imported from your current environ-
	     ment.  Environment	variables may be set or	overridden from	the
	     login class capabilities database according to the	class of the
	     target login.  The	invoked	shell is the target login's, and su
	     will change directory to the target login's home directory.
	     Resource limits and session priority are modified to that for the
	     target account's login class.

     -	     (no letter) The same as -l.

     -m	     Leave the environment unmodified.	The invoked shell is your
	     login shell, and no directory changes are made.  As a security
	     precaution, if the	target user's shell is a non-standard shell
	     (as defined by getusershell(3)) and the caller's real uid is non-
	     zero, su will fail.

     -s	     Set the MAC label to the user's default label as part of the user
	     credential	setup.	Setting	the MAC	label may fail if the MAC
	     label of the invoking process is not sufficient to	transition to
	     the user's	default	MAC label.  If the label cannot	be set,	su
	     will fail.

     The -l (or	-) and -m options are mutually exclusive; the last one speci-
     fied overrides any	previous ones.

     If	the optional args are provided on the command line, they are passed to
     the login shell of	the target login.  Note	that all command line argu-
     ments before the target login name	are processed by su itself, everything
     after the target login name gets passed to	the login shell.

     By	default	(unless	the prompt is reset by a startup file) the super-user
     prompt is set to ``#'' to remind one of its awesome power.

     Environment variables used	by su:

     HOME  Default home	directory of real user ID unless modified as specified

     PATH  Default search path of real user ID unless modified as specified

     TERM  Provides terminal type which	may be retained	for the	substituted
	   user	ID.

     USER  The user ID is always the effective ID (the target user ID) after
	   an su unless	the user ID is 0 (root).

     /etc/pam.d/su  PAM	configuration for su.

     su	-m operator -c poweroff
	    Starts a shell as user operator, and runs the command poweroff.
	    You	will be	asked for operator's password unless your real UID is
	    0.	Note that the -m option	is required since user ``operator''
	    does not have a valid shell	by default.  In	this example, -c is
	    passed to the shell	of the user ``operator'', and is not inter-
	    preted as an argument to su.
     su	-m operator -c 'shutdown -p now'
	    Same as above, but the target command consists of more than	a sin-
	    gle	word and hence is quoted for use with the -c option being
	    passed to the shell.  (Most	shells expect the argument to -c to be
	    a single word).
     su	-m -c staff operator -c	'shutdown -p now'
	    Same as above, but the target command is run with the resource
	    limits of the login	class ``staff''.  Note:	in this	example, the
	    first -c option applies to su while	the second is an argument to
	    the	shell being invoked.
     su	-l foo
	    Simulate a login for user foo.
     su	- foo
	    Same as above.
     su	-   Simulate a login for root.

     csh(1), sh(1), group(5), login.conf(5), passwd(5),	environ(7),

     A su command appeared in Version 1	AT&T UNIX.

FreeBSD	Ports 11.2		August 11, 2013		    FreeBSD Ports 11.2


Want to link to this manual page? Use this URL:

home | help